Astaxanthin is a kind of carotenoid like β-caretinoid, and is a red pigment present in a wide variety of edible creatures living in the nature, particularly, in the ocean, including shellfishes such as shrimp and crab, fishes such as sermon and sea-bream, algae such as green algae Haematococcus, and yeasts such as red yeast Phaffia. 
It has been recently found that astaxanthin has a strong antioxidative action, which is 100 to 1,000 times as high as vitamin E (α-tocopherol) and about 40 times as high as β-carotene. Astaxanthin, which has been conventionally treated merely as a pigment, but is now expected as healthy foodstuff. Many reports inform that astaxanthin has other actions besides the actions mentioned above, for example, anti-inflammatory action, anti-arteriosclerotic action, anti-diabetic action, protecting action of the retina against light damage, circadian rhythm control action, immunopotentiation action, anti-stress action, action of improving muscular endurance, action of improving sperm quality, and action of suppressing induction of bladder cancer. It is also reported that astaxanthin is effective for the skin since it has an action of suppressing pigment deposition, melanogenesis, and optical aging.
Recently, with growing interest in pets, in particular, growing number of indoor pets, health, appearance and behavior of pets have caused problems that affect the owners. The problems, which are particularly caused by environments and feeding conditions of pets, include sleep disorder, deterioration of sensibility such as perception and cognition and visual sense, odor emitted from excrement such as feces and urine, and symptoms of diseases such as diabetes and diabetic complications. These symptoms and conditions of pets have been controlled by medication. However, the symptoms and conditions are chronic and side effect caused by medication is a matter of concern. For these reasons, it has been desired to develop a something derived from a nontoxic substance, that is, naturally occurring substance, having a therapeutic/preventive/improvement effect on the symptoms and conditions. Up to present, astaxanthin and/or an ester thereof has not yet been known to have effects of deodorizing excrement such as urine and feces, improving sleep, sensibility such as perception and cognition and visual sense, and an effect of treating, improving or preventing diabetes and diabetic complications of pets.
Recently, with growing number of singles, elderly persons and nuclear families in our country, the number of families having a pet as well as the number of indoor pets are increasing. In the circumstance, odor emitted from excrement such as feces and urine is a problem for owners. Odor complaints, which have been mostly directed to odor of apartment houses and family-owned houses, now increasingly directed to urban life. In these circumstances, it has been strongly desired to develop pet food safe and effective in deodorizing excrement.
As examples of pet food effective in deodorizing excrement, there are a fermented healthy feed containing a solution of a fermented product by Bacillus subtilis and a tree extract (see Patent Document 1); a fecal odor deodorant for domestic animals containing a copper chlorophyllin salt as an active ingredient (see Patent Document 2); a feed effective in deodorizing animal excrement containing an extract from cinnamon leaves with a water/methanol mixture solution (see Patent Document 3); and a composition for deodorizing excrement containing a type of lactobacillus and a tea extract (see Patent Document 4).
By virtue of advance in medical technology and improvement of indoor conditions, the life time of pets is extended. With the increase of the lifetime, aging of pets comes to be a matter of concern. In addition, the circadian rhythm of pets is frequently disturbed by people's activity, that is, keeping late and irregular hours, with the result that the pets increasingly suffer from a sleep disorder. The sleep disorder of a pet not only damages pet's health but also disturbs owner's good sleep since the pet and the owner have different life patterns (rhythm of life).
As pet food effective in improving sleep, mention may be made of a composition constituted of tryptophan and a carbohydrate, for facilitating animal sleep (see Patent Document 5); a pharmaceutical composition containing a novel melatonin derivative as an active ingredient, for treating a mammalian sleep disorder (see Patent Document 6); and a pharmaceutical composition containing an acetylcholinesterase inhibitor, for treating an age-related behavior disorder of a pet animal (see Patent Document 7).
When the sensibility of a pet such as perception and olfactory deteriorate with aging, diseases, or a disorder of rhythm of life by urbanization of living environment, the pet is known to become no longer adorable. Patent Document 7 teaches that an acetylcholinesterase inhibitor is administered to improve the sensibility of a pet.
To improve the visual sense of a pet, a method of using astaxanthin and/or an ester thereof to treat retinopathy is known (see Patent Document 8) and an eye control improver containing astaxanthin and/or an ester thereof is known (see Patent Document 9). Furthermore, it has been reported that a food or drink containing astaxanthin and/or an edible ester thereof, for preventing cataract or suppressing progress thereof, is capable of suppressing not only onset of cataract or suppressing progress thereof but also disorders such as monocular diplopia, eye fatigue, and halation, associated with visual disorder due to cataract (see Patent Document 10).
The number of pets suffering from diabetes has been increased by the reasons that the number of pets increases, the living environment of a pet changes, and excessive food is given by the owner of lack of knowledge. Diabetes is mostly developed by a genetic reason. Besides this, diabetes is triggered by an elevated blood glucose level, which is caused by excessive feeding and living habits of indoor life, shortage of exercise, and accompanies various types of complications. It is difficult to limit the amount of a meal in view of the eating habit of a pet as well as to inject insulin to the pet. Administration of medicament may cause harmful effects in various ways. In these circumstances, it is desired to develop food containing a naturally occurring nontoxic substance for treating, improving or preventing diabetes and diabetic complications.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 5-192087    [Patent Document 2] Japanese Laid-Open Patent Publication No. 3-266943    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2001-258480    [Patent Document 4] Japanese Laid-Open Patent Publication No. 2002-114690    [Patent Document 5] Japanese Laid-Open Patent Publication No. 58-201715    [Patent Document 6] Japanese Laid-Open Patent Publication No. 7-196493    [Patent Document 7] Japanese Laid-Open Patent Publication No. 2000-309545    [Patent Document 8] U.S. Pat. No. 5,527,533    [Patent Document 9] International Publication WO 02/094253    [Patent Document 10] Japanese Laid-Open Patent Publication No. 10-276721